Employees evacuated to the roof of the D.C. office building, while hazmat crews inspected the office, spokesman Alex Conant told ABC News. The Fire Department and FBI also responded to the scene.

D.C. Metro Police told ABC News they responded to the scene after receiving a call from Rubio's campaign office that it had received an envelope with a white substance in it. After the powder was tested and deemed non-threatening by the fire department, employees were allowed back into the office.

Rubio, who is in Florida while his home state heads to the polls in the presidential primary contest, expressed his gratitude to D.C. emergency personnel in a tweet.